The P-51H was the final production Mustang and used the new V-1650-9 engine, a version of the Merlin that included Simmons automatic supercharger boost control with water injection, allowing War Emergency Power as high as 2,218 hp. With the new airframe, the extra power and a more streamlined radiator, the P-51H was among the fastest propeller fighters ever, able to reach 784 km/h.
The P-51H was designed as the primary aircraft for the invasion of Japan, with 2,000 ordered to be manufactured at Inglewood. Production was just ramping up with 555 delivered when the war ended.
Although some P-51Hs were issued to operational units, none saw combat in World War II, and in postwar service, most were issued to reserve units. One aircraft was provided to the RAF for testing and evaluation. The P-51H was not used for combat in the Korean War.